1. Field of the Invention
This invention relates to internal combustion engines with superchargers, and more particularly to an internal combustion engine with a supercharger of the type in which actuation of the supercharger is controlled depending on the operating conditions of the engine.
2. Description of the Prior Art
Several types of superchargers for internal combustion engines are nowadays available which include superchargers of the mechanical type, exhaust-turbo-type and exhaust-pressure-wave type. The supercharger that is most widely used is of the exhaust-turbo-type. In internal combustion engines with superchargers of the prior art, the supercharger is actuated to perform its function over a range of engine operations beginning with the throttle valve in a half-open position and ending with the throttle valve in a full-open position, and more supercharging pressure than is necessary is allowed to escape through a suction bypass or an exhaust bypass, to enable a desired engine power to be developed at full-open throttle.
It is not advisable to effect supercharging of the internal combustion engine over the entire range of engine operations, for the reasons stated hereinafter. In the case of a supercharger of the exhaust-turbo-type, for example, the air drawn into the engine that is pressurized would be throttled by the throttle valve when the engine is operating at half-open throttle, making a supercharging operation meaningless. In a supercharger of the exhaust-turbo type, exhaust gases are passed through an exhaust turbine to boost engine power, and this causes an increase in the pressure of exhaust gases. At the same time, a rise in temperature due to compression by supercharging takes place in the air drawn through a suction system. These phenomenons combine to reduce the efficiency with which the air intake is supplied to the engine and reduce the expansion ratio, resulting in a reduction in the power developed by the engine. In addition, in a spark-ignition type engine, knocking is liable to occur when these phenomenons appear, and a lag of ignition becomes inevitable. Thus, the power developed by the engine is reduced after all, with no desired effects of supercharging being achieved. Moreover, supercharging of the engine over the entire operating conditions thereof applies loads to the supercharger body, exhaust system and suction system at all times, thereby reducing the reliability of the supercharger in performance and shortening the service life thereof.